The quality of materials used in road infrastructure and the grain size distribution of the materials are very important for road construction works. In many projects, appropriate road materials cannot be found easily around the project area and this increases the cost of projects. In this study, polymer was used as an additive for the improvement of a base material for road infrastructure. Working in the framework of a divided road in Kesan Uzunkopru (20(th) km), polymer was implemented in 100-m section at 1% of the dry weight of soil. Plate loading tests and field CBR tests were conducted on both of polymer; improved base and natural base without additive, and comparisons were made. In the plate loading tests, the maximum deformation decrease from 3.8 - 1.7 mm and permanent deformation decrease from 2.1 - 1.1 mm with polymer additive under very high stresses such as 1 MPa. Sieve analysis results showed that polymer binds and agglomerates the finer particles in the material and the finer content in the material drops from 7 - 1% with polymer. These types of improvements will allow the use of formerly unsuitable material in road construction works.